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Date: Fri, 17 Jan 2014 15:09:39 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: mingo@...nel.org, linux-kernel@...r.kernel.org,
linaro-kernel@...ts.linaro.org, alex.shi@...aro.org
Subject: Re: [PATCH 4/4] sched: Idle task shortcut optimization
On Fri, Jan 17, 2014 at 10:04:04AM +0100, Daniel Lezcano wrote:
> + schedstat_inc(rq, sched_goidle);
> +#ifdef CONFIG_SMP
> + /* Trigger the post schedule to do an idle_enter for CFS */
> + rq->post_schedule = 1;
> +#endif
> + return rq->idle;
Urgh, that retains the stupid idle crap like it is.
I've not yet tested this, but is there a reason something like the below
couldn't work?
---
Subject: sched: Clean up idle task SMP logic
From: Peter Zijlstra <peterz@...radead.org>
Date: Fri Jan 17 14:54:02 CET 2014
The idle post_schedule hook is just a vile waste of time, fix it proper.
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
---
kernel/sched/fair.c | 5 +++--
kernel/sched/idle_task.c | 21 ++++++---------------
2 files changed, 9 insertions(+), 17 deletions(-)
Index: linux-2.6/kernel/sched/fair.c
===================================================================
--- linux-2.6.orig/kernel/sched/fair.c
+++ linux-2.6/kernel/sched/fair.c
@@ -2416,7 +2416,8 @@ void idle_exit_fair(struct rq *this_rq)
update_rq_runnable_avg(this_rq, 0);
}
-#else
+#else /* CONFIG_SMP */
+
static inline void update_entity_load_avg(struct sched_entity *se,
int update_cfs_rq) {}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
@@ -2428,7 +2429,7 @@ static inline void dequeue_entity_load_a
int sleep) {}
static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
int force_update) {}
-#endif
+#endif /* CONFIG_SMP */
static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
Index: linux-2.6/kernel/sched/idle_task.c
===================================================================
--- linux-2.6.orig/kernel/sched/idle_task.c
+++ linux-2.6/kernel/sched/idle_task.c
@@ -13,18 +13,8 @@ select_task_rq_idle(struct task_struct *
{
return task_cpu(p); /* IDLE tasks as never migrated */
}
-
-static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
-{
- idle_exit_fair(rq);
- rq_last_tick_reset(rq);
-}
-
-static void post_schedule_idle(struct rq *rq)
-{
- idle_enter_fair(rq);
-}
#endif /* CONFIG_SMP */
+
/*
* Idle tasks are unconditionally rescheduled:
*/
@@ -37,8 +27,7 @@ static struct task_struct *pick_next_tas
{
schedstat_inc(rq, sched_goidle);
#ifdef CONFIG_SMP
- /* Trigger the post schedule to do an idle_enter for CFS */
- rq->post_schedule = 1;
+ idle_enter_fair(rq);
#endif
return rq->idle;
}
@@ -58,6 +47,10 @@ dequeue_task_idle(struct rq *rq, struct
static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
{
+#ifdef CONFIG_SMP
+ idle_exit_fair(rq);
+ rq_last_tick_reset(rq);
+#endif
}
static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
@@ -101,8 +94,6 @@ const struct sched_class idle_sched_clas
#ifdef CONFIG_SMP
.select_task_rq = select_task_rq_idle,
- .pre_schedule = pre_schedule_idle,
- .post_schedule = post_schedule_idle,
#endif
.set_curr_task = set_curr_task_idle,
--
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